1. Field of the Invention
This invention relates to light emitting compositions and light-emitting devices that include the light-emitting compositions. Specifically, this invention relates to light emitting compositions that are printable and light-emitting devices that include iridium-functionalized nanoparticles.
2. Description of the Related Art
Organic Light Emitting Diodes (OLEDs) can be composed of small molecule or polymeric fluorescent or phosphorescent compounds. OLEDs comprise a cathode, a hole transporting layer, an emissive layer, an electron transporting layer and an anode. OLED devices emit light as a result of recombination of positive charges (holes) and negative charges (electrons) inside an organic compound (emissive) layer. This organic compound is referred as an electro-fluorescent material or electro-phosphorescent material depending on the nature of the radiative process. As OLED devices have developed to increase luminousity and increased lifetimes, additional layers, such as hole blocking layers and electron blocking layers, have been incorporated into the OLED device. However, introducing more layers of materials has made the OLED structure increasingly complex. This increased complexity makes the fabrication process significantly more difficult. The addition of layers also makes fabrication more difficult because poor control of layer thickness may impair performance. Thus, improving the performance of OLEDs is often tedious, difficult, and expensive.
There are several methods for manufacturing these above described layers within an OLED device. Primary methodologies include dry processing and wet processing. Dry processing is processing performed without a liquid. Examples of a dry processing operation include dry etching, laser ablation, chemical vapor deposition and vacuum deposition. Dry processing methods have several drawbacks, including difficulty controlling the thickness or composition of a previously deposited layer during serial deposition, high cost of equipment set up and maintenance, slow processing, and difficulty with substrates having a large area. Thus wet production methods may offer significant advantages.
Solution or wet-processing includes the dissolution or suspension of the precursor materials in a solvent and the application of the solution to the desired substrate. Exemplary methodologies include spin coating and inkjet applications. Spin coating can be undesirable because large quantities of the dissolved solution are spun off of the desired surface during the coating process. Thus, large amounts material is wasted production costs are higher.
Inkjet fabrication is less expensive. Inkjet fabrication also allows fine patterning in a simple manner and in a short time. Furthermore, it provides better control of luminescent characteristics such as color balance and brightness (luminance) because the thickness of the layer is easily controlled through adjustment of the discharge amount of the ink or by adjusting the ink concentration.